1. Technical Field
The present invention relates to a light output apparatus and an image display system.
2. Related Art
There is a known coordinate input apparatus of related art that detects the position of a pointing device (pen or user's finger, for example) operated within a predetermined coordinate input area. A proposed example of a coordinate input apparatus of this type forms a light layer along a display surface on which an image is displayed and detects a position where the light is reflected off a pointing device when a predetermined position on the display surface is pointed with the pointing device for detection of the position pointed with the pointing device (see Japanese Patent No. 4,757,144, for example).
The coordinate input apparatus described in Japanese Patent No. 4,757,134 includes a coordinate input effective area that forms a display surface (display screen) of a display apparatus, a plurality of sensor units, a retroreflector provided along three outer sides of the coordinate input effective area and reflects incident light, and a control and computation unit. Each of the sensor units includes a light projection section that forms a light layer along the coordinate input effective area and a light reception section that receives light, and the light projection section has two infrared LEDs (light emitting diodes) each of which emits infrared light and two projection lenses each of which projects the infrared light over a range of about 90°.
The plurality of sensor units are formed, for example, of two sensor units that are disposed in positions in the vicinity of opposite ends of one of the four outer sides of the coordinate input effective area, which has a rectangular shape.
In the coordinate input apparatus, the plurality of sensor units detect a region where the light amount distribution changes in response to the action of a pointing device within the coordinate input effective area, and the control and computation unit calculates the coordinates of the pointing device in the coordinate input effective area based on the number of regions where the change occurs and the number of pen-down actions of the pointing device.
In the coordinate input apparatus described in Japanese Patent No. 4,757,144, however, since in each of the LEDs used in each of the light projection sections, the emitted light spreads as it travels, the emitted light spreads also in a direction away from, the display surface, and the light from the infrared LED may therefore not be effectively used. As a result, the coordinate input apparatus described in Japanese Patent No. 4,757,144 may undesirably be incapable of detecting the position of the pointing device in a stable manner. Use of high-intensity LEDs to avoid the problem described above may result in an increase in power consumption and malfunction in detection due to an increase in difference in optical intensity between an area where light fluxes emitted from the two LEDs overlap with each other and an area where no overlap occurs.
Further, when the coordinate input effective area is formed of a projection surface on which a projector or any other apparatus projects an image, a variety of projection surfaces of different sizes are used, which requires adjustment of the positions of the plurality of sensor units in such a way that the light fluxes from the LEDs travel a Long the entire coordinate input effective area in correspondence to an employed projection surface. Moreover, in the coordinate input apparatus described in Japanese Patent No. 4,757,144, which includes the retroreflector, the retroreflector needs to be so configured that it can handle projection surfaces (coordinate input effective areas) of different sizes. As described above, the coordinate input apparatus described in Japanese Patent No. 4,757,144 has a problem of a complicated structure in the case where the coordinate input effective area is formed of a projection surface.